Not sure if it's actually true but discussions about them would suggest that dirt bikes and street bikes with two strokes like the NSR don't have the same reliability. I see a lot of seized piston threads on dirt bike forums but not so much on forums where street 2 strokes predominate.
Is it the use of premix and the pursuit of crazy fuel/oil ratios that cause what appear to be an inordinate amount of lubrication-based failures on the dirty bikes?

I have ridden both a CRM250 and an NSR50 and each failed but it was jetting issues and stupidity on the NSR and overheating and stupidity on the CRM. Anybody else seeing a pattern? I retained the oil injectors on both and do not look foward to messing with premix if i don't have to.

I see dirt guys measuring rebuild cycles in hours. I ride my bike daily, maybe 45 minutes a trip twice a day and it's going strong. I would be doing a top end rebuild once a week at that level of frequency.

Is it the oil injection and proper maintenance that is keeping it alive or are perhaps motors destined for street bikes a little less ragged edge in the way they are designed and tuned from the manufacturer?

o o


Last edited by DifferentStrokes on Mon Sep 28, 2009 7:23 pm; edited 1 time in total

That's how I messed up my CRM. I was racing a guy and had the throttle locked back for a couple of kilometers. When I rolled off it started smoking bad. Still had really good power but I knew what it was like before, more and pretty clean running. Me mechanic chastised my severely.
I still keep the speedo at the top on the NSR but I never leave it wide open for more than a few seconds. I modulate it up an down a bit, not sure if it helps though.

I think you will see lots of seized piston threads on dirt bike forums because they (well the 125s) spend almost all there time at full throttle, add to that much more marginal jetting, poor maintenance, dirt getting in when the air filters changed and you end up with seizure. Look after them properly and they don't normally give problems ( crank rebuild at 80 hours, piston at 10-15).

Remember most dirt bikes are designed for competitive racing, the NSR is a road bike. Yes seizure is caused by lubrication failure but if you have been racing in the sand on your MX bike and its boiled over ( no temperature gauge) the first you will know anything is wrong is when its locked up, if you have no coolant then no amount of 2 stroke oil will save your piston.

Standard NSRs should be fine for 45 minute commute, make sure your oil pump is adjusted correctly,warm her up before thrashing, keep up with the maintenance and hopefully you should have a reliable bike.

I wouldn't fear keeping the NSR wide open for a long time, that's what its designed to do and its much more fun that way.

As for dirt bikes coming in a higher state of tune, not really, Tbm magazine tested a standard 07 KTM 125 exc at 28 hp with the off road tyres on so lets say 30 hp with street tyres, that's half of a derestricted NSR.

Your smokey CRM sounds normal to me, when you give a 2 stroke a good run it burns of all the unburnt oil in the exhaust and makes clouds of smoke.

Im a bit confused
You said you had it pinned, backed off and it WAS SMOKEY ? This to me does not indicate a failure. That should be a good sign. Bad if its a 4-stroke, excellent for a 2-stroke. Means there is plenty of oil in there.
2-stroke kart engines have alot of seizures. They are probally the most stressed 2-stroke engine out the box. Some of the faster motor rev to 18000 plus RPM !! Common to see at the end of the back straight, off the gas seizures, because when you shut the throtle, you loose nearly all fuel (and oil) in the engine.
Dirt bike motors also get thrashed. Image the shock on the motor when landing a jump on full throtle, and it pulls the motor down from 10000 to 6000 in a fraction of a second. Acelleration and decelleration of the piston from one extreme to the other would shorten engine life too. A street bike generally would not see that sort of thing.
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Winning isn't everything, but loosing isn't anything

I don't mean standard 2-stroke smoke, we are talking spyhunter smokescreen here. I've had good results from all my Hondas. Like I said, both failures I blame on myself. The NSR failure was actually kind of funny. I had the throttle cranked back and the bike started to hesitate then POP! The engine noise was gone like you flipped a switch and all I heard was the chain rolling across the sprockets as the bike coasted to a stop.
I stood on one peg and with the other foot turned it into a kick scooter for a couple of kilometers to the house and pulled the plug. I shone a flashlight in it to see what I could see. Well the top of the connecting rod looks good. wait, what did I just see?!
Yup, blew a hole clean through the piston crown.



A high comp piston, colder plug and rejet fixed the problem. Oh yeah, I also learned when the bike is acting weird BACK OFF AND CHECK IT OUT!

Looks just like my MBX125 did all those years ago! That was on the edge and pinned at the time!

The engine noise was gone like you flipped a switch and all I heard was the chain rolling across the sprockets as the bike coasted to a stop.

Ahh yes, been there, done that too! Not funny at the time, but funny to reflect back on it.
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Andy.
NSR-WORLD.COM

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